Prosthetic heart valve

ABSTRACT

Bi-leaflet and single occluder heart valves have improved pivot arrangements that create quick valve response to flow reversal and minimize impact. Valve members or occluders, which are slidably and pivotally mounted in a heart valve body, can be aligned precisely parallel to blood flow in the open position. Lugs on the valve members engage surfaces on projections extending radially inward from flat wall sections in the valve body sidewall, and the shape and relationship of these interengaging surfaces provide prompt initial rotation, low wear and reduced impact upon closing. Laterally directed ears engage the valve body arcuate sidewall and assist in defining the path of closing movement.

BACKGROUND OF THE INVENTION

The present invention pertains to heart valve prostheses and inparticular, to prosthetic heart valves having valve members which bothpivot and translate, including single occluder and bi-leaflet valves.

DESCRIPTION OF THE PRIOR ART

Various types of heart valve prostheses have been developed whichoperate hemodynamically as a result of the pumping action of the heart.Such heart valves include valves having single occluders which pivotalong an eccentric axis (or both pivot and translate), to open and closethe blood flow passageway, such as those described in U.S. Pat. Nos.3,546,711, 4,011,601, 4,425,670 and 4,725,275, and also includebi-leaflet heart valves, such as those described in U.S. Pat. Nos.4,078,268, 4,159,543 and 4,535,484. The above-mentioned patentsillustrate various different arrangements for pivotally connecting valvemembers (i.e. occluders) to valve bodies and disclose occluders of avariety of shapes. However, most of these designs have never becomecommercial because of some shortcoming, and the need continues forimproved prosthetic heart valves for permanent implantation into thehuman heart.

In its open position, a prosthetic valve should provide a passagewaywhich is large and which has good flow characteristics so that bloodflows freely therethrough without adverse boundary layer separation andwith a minimum of drag. The heart valve should be responsive to bloodflow to open quickly during the pumping stroke of the heart and to closequickly when the heart relaxes, to prevent any substantial regurgitationof the blood. The opening and closing of the valve should besufficiently soft so that the patient is not disturbed by the soundsproduced. The heart valve must, of course, be made of materials that arebiocompatible and thromboresistant, and in this regard, it is importantthat all surfaces be well washed by blood to prevent stagnation whichmight lead to eventual clotting. Furthermore, the action of the valveshould be such that it does not cause hemolysis (damaging of bloodcells), and of course, the heart valve should be constructed towithstand countless openings and closings and should not be prone to thecreation of particular regions of wear.

SUMMARY OF THE INVENTION

The present invention provides heart valves having the aforementioneddesirable characteristics wherein the valve member or occluders aredesigned to promptly open and close in response to reversal of the flowof blood, while providing a particularly low-resistance flow path in theopen position, thereby resulting in excellent operating characteristics.The foregoing characteristics are obtained in certain particularlypreferred versions where the occluder or occluders assume an orientationthat is parallel, or nearly parallel, to the direction of blood flow inthe open position, thus allowing particularly efficient blood flowtherethrough in a downstream direction.

The valves each have a generally annular valve body formed with aninterior sidewall, which defines a central passageway therethrough forthe passage of blood in a downstream direction. One or more occludersmounted in the valve body to alternately permit the flow of bloodtherethrough in a downstream direction and block blood flow in thereverse direction utilizing a pivot arrangement which includesprojections extending inward from the valve body sidewall that coactwith lugs formed on the occluder(s). These projections are preferablyformed with first and second flat surfaces which are oriented torespectively lie in juxtaposition with complementary occluder surfaceswhich may be on the lugs, in both the open and closed positions.

In another aspect, each of the projections is formed with at least oneflat surface that is parallel to the centerline of the flow passagewaythrough the valve body. In this instance, such surfaces are positionedso that, when an occluder is in the open position, this flat surface isin juxtaposition with a complementary flat surface portion of theoccluder whereby the downstream flow of blood through the valve bodyfinds the occluder disposed substantially parallel to blood flow, thusproviding minimum resistance to blood flow; the reverse flow of blood inan upstream direction, however, causes upstream displacement such thatthe lugs engage the projections and cause the occluder to promptly beginto pivot toward its closed position.

In a further aspect, the design can be such that the center of rotationcf the pivot (CRP) is initially spaced beyond the outflow surface of theoccluder, to provide for a high initial pivot moment. However, it thenshifts to a location generally near the inflow surface, reducing thepivot moment and providing for a soft final closing movement.

In still another aspect, the pivot design in a bi-leaflet valve can besuch that, at about the instant of closing, when there is first contactbetween the arcuate downstream edge of a leaflet and the valve bodysidewall, all of the forces acting upon the leaflet (when viewed in a2-dimensional projection) intersect near a common point. As a result,the pressure load is most efficiently carried (i.e., the load on theupstream pivot is a minimum for any given pressure acting upon thedownstream surface of the leaflet), and thus wear at this point is alsominimized. Moreover, by offsetting the surface slightly, i.e., up toabout 10°, there can be a small resultant force continuing to cause theoccluders to pivot in a direction so as to assure that the mating edgesof the leaflets abut.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bi-leaflet heart valve embodyingvarious features of the present invention, shown in its open position;

FIG. 2 is an enlarged cross-sectional view of the heart valve takenalong the line 2--2 of FIG. 1, showing the valve with the right handleaflet in its open position and with the left hand leaflet shown inelevation and in its closed position;

FIG. 3 is a partial plan view of the bi-leaflet heart valve shown inFIG. 1 with one leaflet removed and one in its open position;

FIG. 4 is a perspective view of a leaflet from the valve shown in FIG.1;

FIG. 5 is a fragmentary bottom perspective view of the leaflet shown inFIG. 4;

FIG. 6 is an enlarged, fragmentary, cross-sectional view similar to FIG.2 showing the leaflets shortly after they have begun to move toward theclosed position;

FIG. 7 is an enlarged, fragmentary, cross-sectional view similar to FIG.6 showing both leaflets in slightly different intermediate positions intheir movement toward the closed position;

FIG. 8 is an enlarged, fragmentary, cross-sectional view similar to FIG.7 again showing both leaflets in slightly different second intermediateposition in their movement toward the closed position;

FIG. 8A is a fragmentary sectional view taken along line 8A--8A of FIG.8;

FIG. 9 is a cross-sectional view of the heart valve of FIG. 1 in theclosed position;

FIG. 10 is a perspective view showing an alternative embodiment of aleaflet which is curved that might be employed in a valve of the generaltype shown in FIG. 1;

FIG. 11 is a front view of the leaflet of FIG. 10;

FIG. 12 is a cross-sectional view of a valve incorporating a pair of theleaflets shown in FIGS. 10 and 11, which view is generally similar toFIG. 2, with the left-hand leaflet shown in elevation;

FIG. 13 is a perspective view, generally similar to FIG. 1, showing avalve body designed for use with a single occluder (without the occluderinstalled);

FIG. 14 is a perspective view of an occluder designed for use with thevalve body of FIG. 13;

FIG. 15 is a fragmentary cross-sectional view of a heart valve utilizingthe components of FIGS. 13 and 14 shown in the open position, with theoccluder shown in elevation;

FIG. 16 is a cross-sectional view of the heart valve of FIG. 15 shown inthe closed position;

FIGS. 17A and B are cross-sectional views similar to FIGS. 7 and 9showing another alternative embodiment of a heart valve having variousfeatures of the invention;

FIG. 18 is a cross-sectional view similar to FIG. 9 showing yet anotheralternative embodiment of a heart valve having various features of theinvention; and

FIG. 19 is a cross-sectional view similar to FIG. 9 showing stillanother alternative embodiment of a heart valve having various featuresof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-9 show one preferred embodiment of a heart valve prosthesisconstructed according to principles of the present invention. The heartvalve, generally designated as 10, is of a bi-leaflet construction, butit will be readily apparent to one ordinarily skilled in the art thatthe principles of the present invention can be applied to a prostheticheart valve of single occluder construction.

Both versions of heart valves have numerous advantages as will bedescribed herein; for example, such heart valves will provide improvedflow characteristics when the valve is in a fully open position. Theysubstantially reduce boundary layer separation at major surfaces of theoccluders, particularly when the occluders are aligned substantiallyparallel to the valve centerline in the open position, thus minimizingdrag, while also providing good wash characteristics so as to preventstagnation. In addition, such heart valves provide a rapid response uponopening and closing, with a relatively small impact when the occluderscontact the valve body so as to reduce hemolysis or like injury to bloodcells flowing through the valve, and regions of potentially substantialwear are also eliminated.

Referring initially to FIGS. 1-9, heart valve 10 includes a generallyannular valve body 12 which carries a pair of pivoting occluders orleaflets 14 that open and close to allow the flow of blood in thedownstream direction of arrows 18 and to prevent any substantialbackflow. Blood flows through passageway 16 which is defined by agenerally cylindrical interior surface or sidewall 20 of valve body 12.The otherwise cylindrical sidewall surface 20 is interrupted by a pairof diametrically opposed, flat wall sections 24. In the general regionof each of these flat wall sections are a first centrally locatedprojection 26 and a pair of flanking second projections 28 which coactto define the generally rotative movement of the leaflets 14 when theleaflets move from the fully open position to the closed position, andvice versa.

As seen in FIG. 1, these sets of projections 26 and 28, which arepositioned at diametrically opposed locations on the valve body, extendgenerally perpendicularly from the surface of the flat wall sections 24.The central projection 26 has two oppositely facing flat surfaces 30aand 30b, each of which is substantially parallel to the valvecenterline, and a second surface 32 which is preferably transverse, e.g.oriented approximately perpendicular to the valve centerline. The edgesbetween these three surfaces are preferably faceted or rounded (see FIG.2). In this embodiment, each of the second projections 28 has a flatsurface 34 which is oriented substantially parallel to the direction ofblood flow, i.e. the valve centerline, and also has a second, transverse(e.g. generally perpendicular) surface 36; these surfaces intersect atwhat is termed a downstream edge 38 of the projection 28 (see FIG. 7)which may be faceted or rounded as shown. The middle section 40 of thecentral projection 26 is preferably concave with respect to thecenterline of the valve body 12 so as to minimize the area impeding theflow of blood through the passageway 16. The second projections 28 taperin thickness (see FIG. 3) so as to blend into the sidewall 20 of thevalve body at their outer extremities, i.e. having front surfaces 42which are flat and generally parallel to the flat wall section 24 of thevalve body.

The outer surface of the valve body 12 is preferably grooved to receivea metal stiffening ring 43 which in turn supports a sewing ring 44 (seeFIGS. 5 and 9). The sewing ring 44 can be of a conventional design aswell known in this art.

Referring now to FIG. 2, the leaflets 14 each have an upstream-facing orinflow surface 46 and an opposed downstream-facing or outflow surface 48(with reference to the leaflets when positioned in the closed position).The leaflets can be essentially flat and thus of substantially uniformcross-sectional thickness, except for side sections 49 located alongeach lateral edge where lugs are formed which coact with the projections26 and 28 to define the opening and closing movements of the leaflets.Alternatively, the leaflets can have considerably different shapes, suchas having a generally cylindrically shaped main body section, asdescribed hereinafter with respect to FIGS. 10-12.

The leaflets 14 each have a major arcuate edge surface 50, which islocated at the downstream edge of the leaflet in its open position, anda minor mating edge surface 52 which is located at the opposite,upstream edge of the leaflet (again, assuming a leaflet in an openposition). The arcuate edge surface 50 preferably has a configuration toabut and seat against the cylindrical sidewall 20 of the valve body inthe closed position. The minor edge surface 52 is preferably of aconfiguration so as to mate with the corresponding mating surface to theopposing leaflet, and this minor surface 52 is oriented at an angle suchthat the two mating edge surfaces of the leaflets 14 abut whileextending across the diameter of the valve passageway when in the closedposition, as is well known in the art of bi-leaflet valves. As seen inFIGS. 8 and 9, each side section 49 has a lower beveled section 52a thatprovides clearance between the two leaflets during their closing andtheir initial opening movements.

Referring to FIGS. 4 and 5, the leaflets 14 each include a pair ofopposed, lateral surfaces 53 which are interposed between the majorarcuate surface 50 and the minor mating surface 52. These lateralsurfaces 53 of the leaflets are preferably flat, and the leaflets areproportioned so as to provide minimal clearance adjacent the flat wallsections 24 of the valve body 12 (see FIG. 3), so as to enable theleaflets 14 to pivot, with these lateral edge surfaces 53 movingadjacent to the flat wall sections 24, one of which is usually servingas a bearing surface.

Referring to FIG. 5, extending from the outflow surface 48 of eachleaflet 14 in each side section 49 is an integral first or opening lug54. These lugs 54 extend in a direction toward the centerline (in theopen position) and have upstream surfaces 52a that are beveled, i.e.slightly angularly offset from the minor edge surface 52; this offsetprevents their interference with each other during closing and openingas indicated above. The lugs 54 have downstream surfaces 56 oriented toengage and lie in juxtaposition with the transverse surface 32 of thecentral projection 26 in the closed position. These surfaces 56 arepreferably oriented at an angle of between about 135° and about 150° tothe flat outflow surface 48, viz. at an angle of between about 30° andabout 45° to the centerline plane in the open position. This downstreamsurface 56 may be formed with a recess 56a which accommodates therounded edge of the projection 26, as seen in FIG. 2, when in the openposition and prevents the leaflet from escaping downstream. As shownhereinafter, the edge of the downstream projection 26 could be faceted.The radially inward-facing surface 55 of each lug 52 is preferablytapered outward toward its base so as to assure the lug has adequatestructural strength, as seen in FIG. 5.

Second or closing lugs 57 are also preferably formed in the sidesections 49 as an integral part of the leaflets 14 and protrude from theinflow surface 46 of each occluder, with one such lug being locatedgenerally along each lateral edge of the leaflet. The second lugs 57each have a front camming surface 59 which is arranged so as to lie at adesired acute angle to the plane of the flat surface of the major bodyportion of the occluder, and can have, as best seen in the right handleaflet of FIG. 2, an extension 57a which is oriented parallel to thecenterline of the valve body when in the open position. These lugs 57which extend in an upstream direction with the leaflets in the closedposition are sometimes referred to as the upstream lugs. The frontcamming surfaces are oriented at an angle of between about 5° and about35°, preferably about 30°, to the centerline plane in the open position.The lug 57 also has a rear angular surface 61 which is oriented at anangle of between about 30° and about 45° to the centerline plane in theopen position so as to lie generally in juxtaposition with thetransverse surface 36 of the projections 28 when the leaflets are in theclosed position. The front camming surface 59 may extend to and meetwith the rear surface 61 as shown in the embodiments in FIGS. 1 through9, or there may be an intermediate surface separating the two or aslight recess at the point of junction, as shown in some of thealternative embodiments described hereinafter.

The radially outer lateral surfaces of the lugs 57 are chamfered neartheir upper ends to provide a small generally triangular surface 63 oneach that generally provides clearance for the lug when it rotates inthe region beyond the flat wall 24 of the valve body 12, as best seen inthe right hand portion of FIG. 2. The chamfer is precisely located (seeleft hand leaflet of FIG. 2) so as to create an upper bearing point orear 63a which engages the curved sidewall of the valve body during anintermediate portion of the closing movement (see FIG. 7) and a lowerbearing point or ear 63b which engages the curved sidewall during thelater stages of the closing movement of the leaflets. These ears assistin guiding the rotation of the leaflets in the closing movement afterthe leaflet has lost sliding contact with the downstream projection 26(which contact is illustrated in FIG. 6); the ears 63a and 63b are bestseen in FIG. 5. There are two lines of contact, or rub lines 65a and bthat extend generally parallel to the centerline of the valve body atthe locations where there can be contact, respectively, between theupper ears 63a and the lower ears 63b with the valve body sidewall, asbest seen perhaps in FIGS. 8 and 8A. The sizing of the leaflets is suchthat contact of the ears on opposite lateral sides of a leaflet and therespective rub lines will not occur simultaneously. This contact betweenthe lower ear 63b and the curved sidewall 20 of the valve body, whichcreates the rub line 65b, is shown in the fragmentary cross-sectionalview 8A.

In addition to these angular surfaces of the lugs, both lugs can includeelongated thickening sections 54a and 57a, respectively, that extendparallel to the inflow and outflow surfaces along the leaflet lateraledges 53. These strengthen the lateral regions or side sections 49 ofthe leaflets where engagement occurs as a result of the pivotingarrangement, while allowing the major body portion of the leaflets 14 toremain relatively thin so it will provide less resistance to blood flow.

The leaflets 14 are installed in the valve body 12 by squeezing the bodyat diametrically opposed locations, i.e. those where the valve body iscut by the reference line 2--2 in FIG. 1. This causes the diametricallyopposed flat wall sections 24 to further separate, thus allowing theleaflets 14 to be fitted into the passageway 16 of the valve body. Theside sections 49 at the lateral edge regions of the leaflets containingthe first lugs 54 and second lugs 57 are received between theprojections 26 and the projections 28 of the valve body. When thesqueezing force is removed, the valve body 12 returns to its originalconfiguration, leaving the desired minimal clearance between the flatwall sections 24 of the valve body 12 and the lateral edge surfaces 53of the leaflets as discussed above. The locations of the projections 26and the projections 28 is such that the leaflets may initially translateslightly but then quickly begin to rotate in traveling from the open tothe closed position, while the leaflets always are maintained infunctional operating attitudes. This is discussed further below inrelation to the operation of the valve.

As will be appreciated by those skilled in the art, the leaflets 14 andheart valve body 12 have relatively simple configurations which are easyto machine; they also provide improved economics of fabrication in thattolerances of the heart valve components are easily maintained. Theleaflets are slidably-pivotally mounted for travel between closed andopen positions, and it is generally preferred that the leaflets 14 areoriented parallel to the valve centerline in the open position to createminimal turbulence and flow separation. The illustrated design allowssuch a precisely parallel orientation t be achieved while still assuringthat the closing movements of the leaflets begin very rapidly as flowreversal occurs. It also allows for the leaflets to be made justslightly longer in length than required to abut each other so that, eventaking manufacturing tolerances into consideration, there cannot be asignificant leak between the mating edges 52. Moreover, the resultanttorque that is driving each leaflet 14 is initially relatively high, butas the leaflet nears its closing end point, it is reduced because of theshortening of the closing moment arm through which the main force acts,which shortening is an inherent feature of the pivot arrangement designand occurs throughout the closing movement. This reduces noise andleaflet impact and wear, and it significantly lowers the tendency forthe leaflets to bounce back upon reaching the closing end points.

For illustration and comparison purposes, FIG. 2 shows the valve 10 withthe left-hand leaflet in the closed position and with the right handleaflet in the full open position, although it should be understood thatsuch an orientation would never occur as the two leaflets 14 movesubstantially simultaneously with each other. In this respect, attentionis directed to FIGS. 6 and 9 of the drawings wherein representativemovement of the leaflets from the open to the closed position isillustrated. FIGS. 7 and 8 show intermediate position with the RH and LHleaflets having different orientations for purposes of explanation.

The fully open leaflet position is shown on the right hand side of FIG.2 wherein the recess 56a of the first lug 54 is in contact with therounded edge between the surfaces 30 and 32 of the first or centralprojection 26. The flat extension portions 54a of the first lugs (alongthe outflow surfaces) are in contact with the surface 30b of theprojections 26 and thus lie substantially parallel to the centerline.The thin parallel extensions 57a of the lug 57 are similarly in contactwith and lie in juxtaposition to the surface 34 of the projection 28(which surface is also parallel to the centerline). Thus, in the openposition, the major body portion of the leaflet extends substantiallyparallel to the valve centerline, thus providing minimum obstruction tothe downstream flow of blood.

Upon the reversal of blood flow as a result of the contraction of theheart, the backflow of blood creates a drag on the surfaces of theleaflet, displacing it upwardly (with reference to FIGS. 2 and 6). Abrief initial movement may be one of pure translation, i.e. all pointson the body are simultaneously moving in the same direction at the samevelocity, with the amount of translation being dependent upon thelocation of the upstream end of the camming surface 59 and the amount oftolerance in the spacing between projections 26 and 28. The presence ofthe front camming surface 59 causes the leaflet 14 to substantiallyimmediately begin to rotate (see FIG. 6) as it continues to slideupward, maintaining contact between the camming surfaces 9 and thecurved edges 38 of the upstream projections 28. During the first phaseof closing movement, contact is likely maintained between the extensionregions 54a of the first lug and the curved upstream edges of the centerprojection 26; however, this contact depends upon the spacing (in thegenerally radial direction) between the central projections 26 and theflanking projections 28 and the dynamic conditions within thebloodstream. This prompt rotation continues to expose the outflowsurface 48 of the leaflet to more and more of the full force of thebackflowing stream of blood, thereby amplifying the rotative forcevector being applied against each leaflet.

Illustrated in FIG. 7 are positions where continued sliding-pivotalmovement has occurred and where the contact of the left hand leaflet 14awith the downstream projection 26 has ended so that further movement isbeing defined by the camming surface 59 and the upper ears 63a, whichhave moved into engagement with the curved sidewall 20 along the rubline 65a the upper end of which is approached. Once the end is reached,the next movement of the leaflet will be defined by the camming surfaces59 and the lower ears 63b which will travel upward along the shorter rublines 65b (which as shown in FIGS. 6 and 7 are located slightly nearerthe valve centerline when projected onto a plane perpendicular to thepivot axis of the leaflet). When the lower ears 63b have nearly reachedthe upper ends of the rub lines 65b, the travel of the camming surface59 along the downstream projection edge 38 is such that the junctionbetween the front and rear surfaces 59, 61 has nearly been reached (asillustrated generally in FIG. 8 with respect to the left hand leaflet).

If external forces upon the patient or dynamic forces within thebloodstream at the valve are such, an intermediate position such as thatillustrated by the right hand leaflet in FIG. 7 may be reached where thesliding-pivoting movement has been such that the junction between thefront camming surface 59 and the rear surface 61 has reached thedownstream edge 38 of the projection 38 without any contact of either ofthe ears 63a,b with the rub lines 65a,b. Thereafter final movement isgenerally one of rotation about a fixed pivot point. As shown in FIG. 8,as this pure rotation of the right hand leaflet 14b continues, theprimary function of the upstream projection 28 is one of pivotal supportfor the leaflet at the junction between front camming surface 59 and therear surface 61, and contact between the lug extensions 54a and thecentral projections 26 has terminated at this stage of the movement. Bycomparing the right hand leaflets 14b in FIGS. 7 and 8, it can be seenthat the outflow surface 48 of the leaflet moves away from the centralprojection 26 as pure rotation begins toward the further intermediatelocation being shown in FIG. 8. Thus, final movement from theorientation of FIG. 7 is generally that of movement about a fixed pivot.

It is anticipated that leaflet movement will generally follow the pathof the left hand leaflets 14a in FIGS. 7 and 8, with the locations ofthe ears 63a and 63b playing a part in defining the precise CRP (centerof rotation of pivot) for each leaflet as the closing movementcontinues. The CRP is located by drawing perpendiculars to the leafletsurface at each point of contact to see where they intersect. The lefthand leaflet 14a in FIG. 8 should continue to travel so that the lowerear 63b reaches the top of the rub line 65b at the same time as thedownstream end of the camming surface 59 reaches the edge 38 of theprojection 28. However, depending upon the extent of the chamfer whichcreates the triangular surface 63, contact between the ear 63a and thesidewall might cease as the leaflets are in their final approach to thefully closed position, which is still acceptable.

The last phase of the movement occurs when the arcuate downstream edge50 (see FIG. 2) of the leaflet makes contact with the interior sidewallof the valve body. Whichever leaflet happens to close first, i.e. itsmajor arcuate edge is the first to contact the sidewall 20, its matingedge surface 52 may extend past the centerline by 1 or 2 thousandths ofan inch, if the manufacturing tolerance is such that it was slightlyoversized; however, such a situation will be accommodated when thesecond of the two leaflets reaches the fully closed position, therebypositively assuring that there is contact between the primary flatfacing surfaces of the mating edges 52 so as to insure against anysubstantial amount of leakage that might potentially result from amismatch of valve components should both coincidentally happen to havebeen sized at opposite ends of manufacturing tolerances--such as ispossible in other mechanical heart valves having different pivotarrangements. FIG. 9 shows the leaflets in the closed position, whereinthey are preferably oriented with their flat main body surfaces 46, 48at an angle of between about 30° and about 45° to the centerline plane.In this position, the surfaces 56 of the lugs 54 are spaced slightlyabove, but in juxtaposition with, the upstream surfaces 32 of thecentral projections 26.

When the next cycle occurs so that there is again a flow of blood in thenormal downstream direction through the valve, the force of the blood onthe inflow surfaces 46 of the leaflets 14 causes immediate displacementslightly downward until the surface 56b of the first or opening lug 54contacts the upstream-facing surface 32 of the center projection 26.This causes pivoting of the leaflets in the opening direction to occur,with such pivoting being primarily guided by the engagement between thesurfaces 56 and 54a of the opening lugs 54 with the center projection 26although there may be some slight, short engagement between the ears 63aand 63b and the valve body sidewall. Such rotation continues until thefully open position is reached with the leaflets 14 in a substantiallyparallel position with respect to the valve centerline. In thisposition, the rounded upstream edges of the projection 26 interengagewith the recesses 56a, and the downstream-facing surfaces 56 of the lugs54 engage the transverse surface 32. The projection side surfaces 30 arealso in juxtaposition with the flat surfaces of the thin lug extensions54a, and the shorter extensions 57a of the upstream lugs 57 lie injuxtaposition with the side surfaces 34 of the upstream projections 28,thus assuring stable support in this open orientation until the nextreversal of blood flow.

A particularly advantageous pivot arrangement is created by the use ofprojections 26, 28 spaced apart in this manner (which extend from thetwo diametrically opposed flat sidewall sections 24 of the valve body)in conjunction with the oppositely extending lugs 54, 57 located alongthe lateral edges of each leaflet. There is a prompt and rapid rotationof the leaflets 14 about a center of rotation of pivot (CRP) thatinitially is spaced a significant distance, preferably at least adistance equal to one-half the radius of the valve passageway, beyondthe outflow surface of the leaflet when closing movement first begins.For example, in FIG. 6, which illustrates the position after a slightamount of rotation has actually taken place, the CRP for the left handleaflet is at point X a substantial distance on the opposite side of thecenterline plane of the valve, i.e. the plane which contains thecenterline of the passageway and is parallel to the axes of rotation ofthe valve members, most preferably this distance is equal to at leasthalf the radius of the passageway. As a result, there is a very largeinitial effective torque which drives the leaflet in its rotationalmovement, achieving a prompt response in moving the leaflets toward theclosed position and minimizing regurgitation of blood. There is also asimilar, large moment arm which contributes to achieving prompt initialrotational movement of the leaflets moving to the open position.However, a further significant advantage is found in this pivotconstruction because the CRP, during closing, moves from its initiallocation, which is not only well beyond the outflow surface of theleaflet but also well beyond the centerline plane for a bi-leaflet valve(thereby encouraging prompt rotational movement as a result of the largemoment arm), to a location generally close to the outflow surface 48 oreven beyond the inflow surface 46 of the leaflet when the leaflets nearthe end of closing rotation. The result of this change in CRP locationis a lessening of the rotational moment arm and a consequent softeningof the final impact of the leaflet against the valve sidewall, therebyreducing both noise and wear.

The term CRP is used to describe the theoretical instantaneous pivotcenter about which rotation of the leaflet is occurring at any instantin its movement from the open position to the closed position, and viceversa. Where there is contact at two locations along each lateral edgeregion of the leaflet, i.e., with the projection 28 and with either theprojection 26 or the valve body sidewall at one of the rub lines 65, theCRP is determined by constructing perpendiculars to the respectivesurfaces of the leaflet at the precise points where contact occurs andthen determining the point where those perpendiculars cross. The CRP isshown for the left hand leaflet in FIG. 6 as point X, in FIG. 7 as pointY and in FIG. 8 as point Z, with the latter two points being close tothe outflow surface 48. On the other hand, when the leaflets shift tothe locations shown for the right hand leaflets 14b in FIGS. 7 and 8.The CRP is thereafter located at the junction between the cammingsurface 59 and the near surface 61, which is slightly beyond the inflowsurface 46.

Comparison will show that there is initially a very large rotationalmoment arm because the CRP was initially spaced a relatively longdistance from the point on the outflow surface of the leaflet whichcorresponds to the point at which a single vector can be applied thatwill be equivalent to the sum of all of the closing (or opening) forcesupon the leaflet. Such a point can be computed to be generally locatedclose to the geographic center of the outflow surface 48 in the latestages of closing, but in the early stage of lift upon a flat plate suchas this, the composite force vector (FV) is computed to act through acentral point located about 25% of the length of the leaflet from theedge 50 which is the leading edge with respect to the backflow of blood.It should be apparent that this moment arm, defined by the distancebetween this point and the CRP, has been considerably shortened in FIGS.7 and 8. Moreover, in FIG. 8, the CRP for the right hand leaflet 14b isat or very near the intersection between the front camming surface 59and the rear surface 61 of the closing lug 57. The result of theshortening of the distance between the CRP and the point at which thecomposite force vector is being applied, as a result of migration of theCRP from a point far beyond the outflow surface (in the direction awayfrom the occluder) to a point near the surface of the leaflet, isparticularly advantageous. It results in a reduction in the closingimpact of the leaflet and also in a reduction of the amount of any finalsliding movement of the leaflet in reaching the closed position at atime when the pressure differential across the leaflet is highest andthus would contribute the greatest to wear.

In addition, as shown with the LH leaflet in FIG. 2, at the point ofclosure, the closing force is represented by the composite closing forcevector FV, and the opposite and equal forces are the force W (at whichthe arcuate edge 50 of the leaflet bears against the cylindricalsidewall of the valve body and the force vector B, which is located atthe point of engagement between the camming surface 59 and thedownstream edge of the projection 28. In the illustrated embodiment, theorientation of the camming surface 59 is such that the force vector B isapplied along a line so that these three forces meet at about a point Qso there is no final closing torque, which as mentioned above, reduceswear.

Shown in FIGS. 10, 11 and 12 is an alternative embodiment of a curvedleaflet 71 which has a convex curved inflow surface 73 and a concavecurved outflow surface 75 that form its main body portion which, insteadof being substantially a flat plate as in the case of the leaflets 14hereinbefore described, is a section of a tube or hollow cylinder ofelliptical or oval cross section. As a result, in the open position, aheart valve 77 using two of these leaflets 71 (see FIG. 12) has anenlarged central flow channel section compared to the valve 10 where twoleaflets 14 having the flat body sections are employed. However, themain body of each leaflet is oriented substantially parallel to thedirection of blood flow and thus again presents minimal resistance.

From the standpoint of guiding the movement of the leaflets 71 betweenthe open and closed positions, a valve body 81, which is of essentiallythe same design as the valve body 12, is employed. Because of therelative location of the pivot arrangement to the main body portion ofthe curved leaflets 71, a central downstream projection 79 is locatedfurther downstream from the upstream edge of the valve body 81 resultingin upstream projections 83 which are elongated although they could beshortened or chamfered at their upper ends. The valve body 81, as shownin FIG. 12 could be shorter in height in comparison to FIG. 2 becausethe downstream arcuate edge surface abuts the valve sidewall at an axiallocation near the leaflet pivot axes. The side sections of the curvedleaflets 71 are shaped to have lugs 85 and 87 which have functional andcamming surfaces 89 that are substantially the same as those describedhereinbefore with respect to the leaflets 14, and as a result, it willbe apparent that the rotational movement of the curved leaflets 71 willbe substantially the same as that hereinbefore described for theleaflets 14 because the side sections have such similar lugs 85, 87.

Consequently, it can be seen that the various advantages of the valveconstruction hereinbefore described are independent of the particularshape of the main body of the leaflets; however, it should be apparentthat the main body portions of the leaflets 71, although curved inprofile, are made up of a locus of straight lines which extend parallelto the centerline of the valve in the open position. Thus, thesetwo-dimensionally curved leaflets 71 having a main body portion that isa section of an elliptical or oval cross section tube (the axis of whichtube is parallel to the valve body centerline in the open position)provide minimal resistance to flow of blood and also minimize flowseparation.

Shown in FIGS. 13-16 is a single occluder version of a heart valve 99embodying various features of the invention which has many of theadvantages that are found in the bi-leaflet versions describedhereinbefore. FIG. 13 shows a valve body 101 designed to accommodate asingle occluder or valve member 103 that will slidably-pivotally movefrom an open to a closed position and vice versa. The valve member 103,shown in FIG. 14, has a flat main body section 105 in the region of thepivots and has a slightly curved downstream section 107 which terminatesin an arcuate edge surface 109 which forms a major portion of thesurface that abuts the valve sidewall, in the region downstream of thepivot axis in the closed position. The lateral edges of the occluder 103are flat surfaces 111 which interconnect the major arcuate edge surface109 and an upstream arcuate edge 113 which abuts the valve body sidewallupstream of the pivot axis when the occluder is in the closed position.The pivot arrangements are similar to those discussed hereinbefore, withlugs 115, 117 being formed in a pair of integral side sections 119 thatflank the main flat body portion 105 of the occluder.

The lugs 115 protrude from what is termed the inflow surface 105a of theoccluder 103 and are sometimes referred to as the upstream or closinglugs because they extend in an upstream direction in the closed positionas seen in FIG. 16. The lugs 115 have a front camming surface 121 whichinitiates the closing rotation and a rear surface 123 which is formed atan obtuse angle to the front camming surface 121. The downstream oropening lugs 117 extend from the outflow surface 105b of the occluderand in the illustrated embodiment are located entirely along the flatlateral edge surface 111. The lugs 117 are preferably slightly chamferedso as to have a slightly angularly oriented lateral surface 125 toprovide clearance and avoid contact with the cylindrical sidewall of thevalve body in the opening and closing movement. The lugs 117 each have adownstream surface 127 oriented to lie in juxtaposition with thetransverse surface of the downstream projection of the valve body in theclosed position. The lugs 117 also have an oblique surface 129 adjacentthereto which is oriented to engage and lie in juxtaposition with thisdownstream projection in the open position, as best seen in FIG. 15.

The valve body 101 is generally annular having a cylindrical sidewallsurface 131 that is interrupted by a pair of diametrically opposed, flatsections 133. In the regions of the flat wall sections, there protrudestherefrom upstream projections 135 and downstream projections 137. Theupstream projections 135 each have a flat sidewall 139 that ispreferably parallel to the centerline through the valve body, and adownstream facing transverse surface 141 which may be perpendicular tothe surface 139. The surfaces 139 and 141 meet along a downstream edge143. The downstream projections 137 each have a flat surface 145 whichis preferably parallel to the centerline plane of the valve and anupstream facing transverse surface 147, which is preferablyperpendicular to the surface 145. In the illustrated embodiment, thesurfaces 145 and 147 are interrupted by an intermediate oblique surfaceor facet 149 which is oriented at angle to the centerline of betweenabout 30° and about 60°.

As illustrated in FIG. 15, when the occluder is in the open position,the oblique surface 129 is in contact with the intermediate surface 149of the downstream projection 137, and the outflow surface 105b of theoccluder lies in juxtaposition with the flat surface 145 of thedownstream projection 137. A portion of the inflow surface 105a of theoccluder also lies in juxtaposition with the flat surface 139 of theupstream projection 135.

In the closed position, as illustrated in FIG. 16, the rear surface 123of each lug 115 lies in contact with the transverse surface 141 of theprojection 135, and the arcuate edges 109, 113 are in contact with thecylindrical sidewall 131 of the valve body. The surface 127 of the lugs117 lies in juxtaposition with the upstream facing transverse surface147 of the downstream projection 137. In pivoting from the open to theclosed position, there is sliding engagement between the camming surface121 and the downstream edge 143 of the upstream projection, and theremay be engagement between the outflow surface 105b of the occluder sidesections and the edge between the surfaces 145 and 149 of the downstreamprojection. In other respects, the guidance of the rotational movementof the occluder is generally the same as hereinbefore described withrespect to the leaflets.

Three alternative embodiments of bi-leaflet valves are shown in FIGS.17-19. These are generally similar in most details to the bi-leafletvalve 10 described with respect to FIGS. 1 through 9. The maindifferences generally lie in the shaping of the projections that extendradially inward from the flat sidewall sections of the valve bodies andin the shaping of the lugs on the occluder side sections thatinterengage with these projections to guide the movement of the leafletsbetween their open and closed positions.

FIGS. 17A and B show a heart valve 151 having a pair of leaflets 153,which are mounted in an annular valve body 155 and which have upstreamor closing lugs 157 that extend from the inflow surface of each leafletor occluder and interengage with an upstream projection 159 duringclosing movement. The lugs 157 have camming surfaces made of differentsections. More specific,.ally, there is an initial camming ramp section161 which is a surface oriented at an angle of about 27° to 29° to thecenterline of the passageway (when the leaflet is in the open position).This section 161 leads to a central arcuate section 163, which in turnleads to a final shallow-inclined ramp section 165, which is a surfaceoriented at about 8° to 10° to the centerline plane of the valve (in theopen position), before reaching the rear section 166.

The proportioning of these leaflets 153 is such and the location of thedownstream edge 167 of the projections (at which edge an intermediatesurface or facet 168 meets the transverse surface 169 and about whichthe final pivoting generally takes place) is such that there is a slightgap between the transverse surface 169 of the projection and the rearlug section 166 (that is located just to the rear of the final cammingsection 165 of the upstream lug). This arrangement allows a positiveclosing torque to be created about the downstream edge 167 (as indicatedby the pair of arrows in FIG. 17B) which assures that the mating edges171 of the two leaflets abut tightly in the closed position.

More specifically, at about the point of closure, the closing force isrepresented by the composite closing force vector FV, and the reactionforces are W (at the location where the arcuate edge of the leafletbears against the cylindrical sidewall 173 of the valve body 155) and B,which is located at the point of engagement between the shallow cammingsurface 165 and the downstream edge 167 of the projection. If theorientation of the camming surface 165 was such that the force vector Bwas applied along the heavy dark line "a", these three forces would meetin a point (as illustrated with respect to the FIG. 2 embodiment), andthere would be no positive closing torque. However, by orienting thefinal camming surface 165 so that the force vector B is offset by up toabout 10° counterclockwise, as shown by the lighter arrow carrying thereference letter b, a positive torque is created which assures that themating edges 171 of the two leaflets will tightly abut each other in theclosed position. As seen in FIG. 17A and FIG. 17B, upstream facingfacets 172 are provided on the downstream projections, oriented at anangle of between about 30° and about 60° (and preferably between about45° and about 60°) to the valve centerline plane. These facets 172 liein juxtaposition to the outflow surface extensions 173 of the openinglugs.

FIG. 18 shows a heart valve 175 which has a pair of leaflets 177 havingsome similarity to that just described with the FIG. 17 embodiment. Morespecifically, each leaflet has an upstream lug 179 formed with a firstor front camming ramp 181 section that has a surface which is orientedat an angle of between about 25° and 30° which section leads to a fairlylengthy arcuate section 183, which in turn leads to a final flat section185 that has a surface which is oriented parallel to the valvecenterline plane (in the open position) and to the flat main bodyportion of the leaflet. There is also a curved transition region 187 atthe junction between this parallel section 185 and the rear section 189of the lug, and in the closed position (illustrated), the curveddownstream edge 191 of an intermediate surface or facet 192 of theupstream projection 193 is received in this curved junction region 187of the leaflet lug. In operation, the leaflets 177 function generallythe same as the leaflets 14 shown and described in FIGS. 1 through 9.The closing rotation is instigated by the sliding engagement of thecamming section 181 along the upstream projection intermediate facet orsurface 192 and the edges thereof, with the continuation of the closingrotation being subsequently determined by the intermediate arcuatesection 183 and the final parallel section 185.

FIG. 19 shows yet another heart valve 201 of bi-leaflet constructionwherein each leaflet 203 has a pair of closing lugs 205 formed withtwo-section camming ramps, i.e. an initial section 207 that has asurface which is oriented at an angle of about 22° to 27°, leading to asecond section 209 that has a surface which is oriented at an angle ofabout 10° to 12° (with respect to the valve centerline plane in the openposition). This second section leads to a concave-curved surface 211which forms the transition to the rear surface 213 of the lug, and thecurvature of this surface is carefully matched so as to be substantiallythe same as the radius of curvature of the downstream edge 215 of theprojection 217. As a result, in the closed position, the downstream edge215 is received in this concave-curved region between the flat rearsurface 213 and the second camming surface section 209, and a stablearrangement is achieved.

Although the invention has been described with respect to a number ofpreferred embodiments, which include the best mode presently understoodby the inventor for carrying out the invention, it should be understoodthat various changes and modifications as would be obvious to one havingthe ordinary skill in this art may be made without departing from thescope of the invention which is defined by the claims appended hereto.

Particular features of the invention are emphasized in the claims thatfollow.

What is claimed is:
 1. A prosthetic heart valve includinga generallyannular valve body having an interior sidewall which defines a centralpassageway therethrough, for the passage of blood in a downstreamdirection, having a centerline extending in the direction of blood flow,occluder means having an inflow surface and an outflow surface which ismounted in said valve body to alternately permit the flow of bloodtherethrough in a downstream direction when in the open position andblock the flow of blood in the reverse direction when in the closedposition, said valve body and said occluder means having a pivotarrangement by which said occluder means is guided in moving betweensaid open position and said closed position, wherein the improvementcomprises said pivot arrangement including at least one pair of firstand second projections extending inward from said valve body sidewalland including first and second lug means on said occluder means forengaging said projections, said lug means protruding respectively inopposite directions, each of said projections being formed with flatfirst surfaces oriented substantially parallel to the centerline of saidcentral passageway and each of said projections also having a secondsurface that is oriented generally transversely to said first surface,and said projections being positioned so that, when said occluder meansis in the open position, oppositely facing surfaces on said occludermeans respectively lie in juxtaposition with said first surfaces of saidprojections and said first lug means engages said first projection inthe general region of said second surface.
 2. A prosthetic heart valveaccording to claim 1 wherein said second surface of said firstprojection which is engaged by said first lug means in said openposition faces generally upstream and wherein, upon reversal of flow ofblood through said valve body, said occluder means is displaced upstreamwith said second lug means engaging said second projection and causingsaid occluder means to promptly begin to rotate toward its closedposition orientation.
 3. A prosthetic heart valve according to claim 1wherein said valve body includes two pairs of first and secondprojections at generally diametrically opposite locations, saidprojections of each pair being spaced from each other so that lateraledges of said occluder means are received therebetween.
 4. A prostheticheart valve according to claim 3 wherein each said second lug meansextends in a direction generally away from said inflow surface of saidoccluder means and contains a first upstream surface oriented at anangle of between about 5° and about 35° to a plane containing said valvecenterline when said occluder means is in the open position and whereinsaid second surfaces of said second projections are located upstream ofsaid second surfaces of said first projections.
 5. A prosthetic heartvalve according to claim 4 wherein said second surfaces of said secondprojections are substantially perpendicular to said first surfacethereof and wherein each said second lug means has a second upstreamsurface which is oriented at an angle of between about 30° and about 45°to the centerline of sand central passageway when said occluder means isin the open position and which generally abuts said second surface ofsaid second projection when said occluder means is in said closedposition.
 6. A prosthetic heart valve according to claim 5 wherein eachsaid first lug means has a surface which is oriented at an angle ofbetween about 135° and about 150° to said outflow surface and whereinsaid first projection means is formed with an intermediate flat surfacebetween each said first surface and said second surface.
 7. A prostheticheart valve according to claim 1 wherein said occluder means is formedwith a generally flat body section and wherein a pair of said first lugmeans are formed at locations generally adjacent said lateral edgesthereof so as to extend from said outflow surface of said body section,said generally flat occluder body section being aligned substantiallyparallel to said central passageway centerline in the open position. 8.A prosthetic heart valve includinga generally annular valve body havingan interior, generally arcuate sidewall which defines a centralpassageway therethrough, for the passage of blood in a downstreamdirection, having a centerline extending in the direction of blood flow,a pair of cooperating occluders, each having an inflow surface and anoutflow surface which are mounted in said valve body to alternatelypermit the flow of blood therethrough in a downstream direction when inthe open position and block the flow of blood in the reverse directionwhen in the closed position, said valve body and said occluders having apivot arrangement by which said occluders are guided in moving betweensaid open position and said closed position, wherein the improvementcomprises said pivot arrangement including first and second projectionmeans extending inward from said valve body sidewall and including firstand second lug means protruding in opposite directions from each saidoccluder for engaging said projection means, each of said projectionmeans being formed with flat first surfaces oriented substantiallyparallel to the centerline of said central passageway and each saidprojection means also having a second surface that is oriented generallytransversely to said first surface, said second projection meansincluding a separate second projection spaced from each of said firstprojection means, and said first and second projection means beingpositioned so that, when each said occluder is in the open position,portions of each said occluder lie in juxtaposition with said firstsurfaces of said first and second projection means and said first lugmeans of each occluder engages said first projection means.
 9. Aprosthetic heart valve according to claim 8 wherein said first lug meansin said open position engages said second surface of said firstprojection means which surface faces generally upstream and wherein,upon reversal of flow of blood through said valve body, each saidoccluder is displaced upstream so that said second lug means of eachoccluder engages one of said second projections causing said occluder topromptly begin to rotate toward its closed position orientation.
 10. Aprosthetic heart valve according to claim 9 wherein said valve bodyincludes a set of said first and second projection means at each of twogenerally diametrically opposite locations, said second projections ofeach said set being located in upstream position with respect to saidfirst projection means and having second surfaces which aresubstantially perpendicular to said centerline, said first and secondprojection means of each said set being spaced from one another so thatlateral edges of said occluders are received therebetween.
 11. Aprosthetic heart valve according to claim 9 wherein each said occluderhas a generally flat body section and wherein a pair of said first lugmeans are formed at locations generally adjacent the lateral edgesthereof so as to extend from said outflow surface thereof, saidgenerally flat occluder body section being aligned substantiallyparallel to said central passageway centerline in the open position. 12.A prosthetic heart valve according to claim 11 wherein said second lugmeans contains a first upstream surface oriented at an effective angleof between about 5° and about 35° to said centerline when said occluderis in the open position and wherein said second surfaces of said secondprojections are located upstream of said second surfaces of said firstprojection means.
 13. A prosthetic heart valve according to claim 12wherein said second surface of said second projection is substantiallyperpendicular to said first surface thereof, and wherein said second lugmeans has a second upstream surface which is oriented at an angle ofbetween about 30° and about 45° to the centerline of said centralpassageway when said occluder is in the open position and whichgenerally abuts said second surface of said second projection when eachsaid occluder is in said closed position.
 14. A prosthetic heart valveincludinga generally annular valve body having an arcuate interiorsidewall which is interrupted by a pair of generally diametricallyopposed flat sections and which defines a central passagewaytherethrough, for blood flow in a downstream direction, having acenterline which extends parallel to blood flow, occluder means havingan inflow surface and an outflow surface which is mounted in said valvebody to alternately permit the flow of blood therethrough in adownstream direction when in the open position and block the flow ofblood in the reverse direction when in the closed position, said valvebody and said occluder means having a pivot arrangement by which saidoccluder means is guided in moving between said open position and saidclosed position, wherein the improvement comprises said pivotarrangement including projections which extend inward form said flatsections of said valve body sidewall and lug means formed upon a surfaceof said occluder means for camming contact with said projections, saidlug means having front and rear sections, said projections beingpositioned so that, when said occluder means is in the open position,portions of the surfaces of said occluder means lie in juxtapositionwith surfaces of said projections, said occluder means and said valvebody having interengaging means which limit further downstream movementof said occluder means in the open position, and said positioning ofsaid projections being such that upstream displacement of said occludermeans upon reverse direction flow of blood causes rotational movement topromptly occur as said occluder means begins to move from the openposition to the closed position, which rotational movement is initiallyat least partially defined by sliding engagement between said frontsections of said lug means and said projections and is subsequently atleast partially defined by engagement between said projections and saidrear sections of said lug means.
 15. A prosthetic heart valve accordingto claim 14 wherein said valve body includes other projections at eachof said flat sidewall sections, said other projections beingrespectively spaced from said projections so that a lateral edge of saidoccluder means is received therebetween, wherein said front section ofeach said lug means is inclined at an angle of between about 5° andabout 35° to said centerline with reference to said occluder means inthe open position, and wherein other lug means projecting from saidoccluder means interengage with said other projections, constitutingsaid interengaging means which limits further downstream movement in theopen position.
 16. A prosthetic heart valve according to claim 15wherein the "CRP" of said occluder means is spaced beyond said outflowsurface of said occluder means a distance equal to at least aboutone-half the radius of said passageway when rotation toward the closedposition begins and wherein the "CRP" shifts substantially as rotationcontinues so that, by the time said occluder means is nearing the closedposition, the "CRP" has migrated to a location generally near saidinflow surface of said occluder means.
 17. A prosthetic heart valveaccording to claim 15 wherein said occluder means is formed with a mainbody section and a pair of flanking side sections with said lug meansand said other lug means being formed in said side sections and facingin opposite directions.
 18. A prosthetic heart valve according to claim17 wherein said side sections also are formed with ears which protrudein generally diametrically opposite directions, said occluder meansbeing proportioned so that ears from only one side section engage saidvalve body arcuate sidewall at a time as said occluder means rotatestoward the closed position.
 19. A prosthetic heart valve includingagenerally annular valve body having an interior sidewall which defines acentral passageway therethrough, for the passage of blood in adownstream direction, having a centerline which extends parallel to thedirection of blood flow, a pair of occluders each having an inflowsurface, an outflow surface, a mating edge surface and an arcuatedownstream edge surface, said occluders being mounted in said valve bodyto permit the flow of blood therethrough in a downstream direction whenin the open position with said mating edges spaced apart from each otherand to alternately block the flow of blood in the reverse direction whenin the closed position with said mating edge surfaces abutting eachother, said valve body and said occluders having a pivot arrangement bywhich said occluders are guided in moving between said open position andsaid closed position, with said valve body having projection meansextending inward from said valve body sidewall, wherein the improvementcomprises each said occluder being formed with a flat camming regiongenerally along said inflow surface located for engaging said projectionmeans so as to guide said occluder in pivoting to the closed position,said projection means being so positioned and said flat camming regionson said inflow surfaces being so inclined that, when each occluderarcuate downstream edge contacts said valve body interior sidewall inits movement toward its closed position, the forces acting upon eachsaid occluder are so aligned that, as a result, there is a smallcomposite force acting upon said occluder which tends to cause saidmating edges to rotate into contact with each other.
 20. A heart valveaccording to claim 19 wherein each occluder has an essentially flat mainbody section on which said inflow surface is formed, which inflowsurface is oriented substantially parallel to said valve body centerlinein the open position and is oriented at an angle of between about 30°and about 45° to a plane perpendicular to said centerline in the closedposition.
 21. A heart valve according to claim 20 wherein said inclinedflat camming regions of said occluders have surfaces which are orientedat an angle of between about 30° and about 5° to a plane containing thecenterline of said valve body when said occluders are in the openposition.
 22. A heart valve according to claim 19 wherein each saidoccluder has a length such that when its arcuate downstream edgecontacts said valve body sidewall, the mating edge surface thereofextends just slightly past the valve centerline.
 23. A prosthetic heartvalve according to claim 19 wherein each said occluder is formed with amain body section and with a pair of flanking side sections with one ofsaid inclined flat camming regions being formed in each of said sidesections.
 24. A prosthetic heart valve according to claim 23 whereinsaid occluder side sections are also formed with ears which protrude ingenerally diametrically opposite directions, each said occluder beingproportioned so that an ear of only one side section at a time engagessaid arcuate valve body sidewall as said occluders rotate toward theclosed position.
 25. A prosthetic heart valve includinga generallyannular valve body having an arcuate interior sidewall which isinterrupted by a pair of generally diametrically opposed flat sectionsand which defines a central passageway therethrough, for blood flow in adownstream direction, having a centerline which extends parallel toblood flow, occluder means having an inflow surface and an outflowsurface which is mounted in said valve body to alternately permit theflow of blood therethrough in a downstream direction when in the openposition and block the flow of blood in the reverse direction when inthe closed position, said valve body and said occluder means having apivot arrangement by which said occluder means is guided in movingbetween said open position and said closed position, wherein theimprovement comprises said occluder means is formed with a main bodysection and with a pair of flanking side sections, said pivotarrangement includes projections which extend inward from said flatsections of said valve body sidewall and includes lug means formed ineach of said side sections for camming contact with said projections,said lug means having front and rear sections, said projections arepositioned so that, when said occluder means is in the open position,portions of the surfaces of said occluder means lie in juxtapositionwith surfaces of said projections, said occluder means side sections andsaid valve body also have interengaging means which limit furtherdownstream movement of said occluder means in the open position, saidpositioning of said projections is such that upstream displacement ofsaid occluder means upon reverse direction flow of blood causesrotational movement to promptly occur as said occluder means begins tomove from its open position to its closed position, which rotationalmovement is initially at least partially defined by sliding engagementbetween said front sections of said lug means and said projections andthereafter is at least partially defined by engagement between saidprojections and said rear sections of said lug means, and said occludermeans side sections are also formed with ears which protrude ingenerally diametrically opposite directions, said occluder means beingproportioned so that an ear of only one of said side sections at a timeengages said valve body arcuate sidewall and thereby partially definesthe path of movement of said occluder means toward the closed position.26. A prosthetic heart valve includinga generally annular valve bodyhaving an interior sidewall which defines a central passagewaytherethrough, for the passage of blood in a downstream direction, havinga centerline which extends parallel to the direction of blood flow, apair of occluders each having an inflow surface, an outflow surface, anupstream mating edge surface and an arcuate downstream edge surface,said occluders being mounted in said valve body to permit the flow ofblood therethrough in a downstream direction when in the open positionwith said mating edges spaced apart from each other and to alternatelyblock the flow of blood in the reverse direction when in the closedposition with said mating edge surfaces abutting each other, each otheroccluder including a main body portion whereon said inflow surface andsaid outflow surface are formed so as to be substantially parallel toeach other and also including a pair of side portions flanking said mainbody portion, which side portions are of a thickness greater than saidmain body portion, said valve body and said occluders having a pivotarrangement by which said occluders are guided in moving between saidopen position and said closed position, said pivot arrangement beingsuch that said occluders can assume an orientation in the open positionwherein said inflow surface and said outflow surface are substantiallyparallel to said valve body centerline, said valve body having aseparate projection associated with each said occluder side portion andextending inward form said valve body sidewall, each said projectionbeing located generally adjacent said upstream edge of said associatedoccluder in its open position, each said occluder side portion beingformed so as to contact and cam against said associated projection whensaid occluder is displaced upstream as a result of the flow of blood inthe reverse direction, and said pivot arrangement also being such thatthere is interengagement between each said occluder side portion andsaid valve body at a location apart from the location of camming contactsuch that said camming contact causes said occluder to begin to swingtoward its closed position orientation promptly upon upstreamdisplacement of said occluder.
 27. A heart valve according to claim 26wherein said occluders are located on opposite sides of the centerlineplane, which plane includes said passageway centerline and is parallelto the axes about which said occluders swing, wherein said associatedprojections are located on the side of each occluder opposite from saidcenterline plane in the open position, and wherein said interengagementis with a surface of said valve body which faces away from saidcenterline plane and is at a location downstream from the location ofsaid camming contact.